This invention is generally directed to toner compositions and developer compositions useful in electrostatographic imaging systems including color imaging processes. More specifically, the present invention is directed to toner compositions containing therein, as charge control agents, certain ion-binding polymers.
Electrostatographic processes, and more specifically the xerographic process, are well known as documented in several prior art references. This process involves development of an electrostatic latent image by applying toner particles to the image to be developed using, for example, cascade development, magnetic brush development, and touchdown development. The toner particles applied can be charged negatively or positively, depending upon the charge deposited on the photoreceptor surface and whether image or background areas are exposed to light. Thus, for example, when it is desired to develop an area which is negatively charged relative to the developer housing bias, the toner particles are positively charged usually by incorporating therein certain charge enhancing additives. In contrast, when developing an area which is positively charged relative to the developer housing bias, the toner particles are negatively charged usually by incorporating therein charge control agents which will cause the toner particles to assume negative charges thereon.
In modern xerographic developers, additives known as charge control agents ("CCAs") are used to modify charge levels, charge distribution, admix characteristics and developer life. Problems accompanying the use of CCAs range from shortfalls in their ability to impact this array of properties In a beneficial manner to incompatibility with other subsystems (e.g., photoreceptor and fuser). Pigments, including carbon blacks, organic and inorganic colorants and magnetic particles (Fe.sub.3 O.sub.4, .gamma.-Fe.sub.2 O.sub.3) tend to have a dominant effect on the charging characteristics of a toner or developer. Accordingly, one of the most significant shortfalls in the use of charge control agents for color xerography is the necessity of formulating different compositions whenever the pigments in the toner are changed. Even with effective charge control agents one is often limited in choice of colorant.
Various toner formulations are known:
Winnik et al., U.S. Pat. No. 5,102,763 (issued Apr. 7, 1992), discloses a dry toner composition which comprises a resin, hydrophilic silica particles having dyes covalently bonded to the particle surfaces through silane coupling agents, and a polymer having at least one segment capable of enhancing the dispersability of the silica particles in the resin and at least one segment capable of adsorbing onto the surface of the silica particles. In one embodiment, the polymer segment capable of adsorbing onto the surface of the silica particles is ionophoric and capable of complexing with a salt, thereby incorporating a toner charge control additive into the polymer.
Tsubuko et al., U.S. Pat. No. 4,925,763 (issued May 15, 1990), discloses a developer which comprises toner particles containing therein at least an ionomer resin, which toner particles may comprise a colorant which is prepared by a flushing method by using a pigment component and an ionomer resin, when necessary, with addition thereto of a humic acid component.
Madeline et al., U.S. Pat. No. 4,925,764 (issued May 15, 1990), discloses positively chargeable toner containing block copolymers, which allegedly improves compatibility with the toner resin. Preferred are block copolymers of styrene with methyl methacrylate and butyl methacrylate as one block and dimethylaminoethyl methacrylate as the other block, quaternized with methyl tosylate or benzyl chloride. Phase separation, if any, is discussed for example in Example V, Comparison V, and Comparison VI.
Madeline et al., U.S. Pat. No. 4,925,765 (issued May 15, 1990), discloses negatively chargeable toner containing block copolymers, which allegedly improves compatibility with the toner resin. Preferred are block copolymers of styrene, methyl methacrylate and butyl methacrylate as one block and salts or esters of methacrylic acid or acrylic acid as the other block in the copolymer.
Smith et al., U.S. Pat. No. 4,592,989 (issued Jun. 3, 1986), discloses a toner composition containing resin particles, pigment particles, and a complex of a dipolar molecule or salt attached to an ionophoric polymer.
Lewis et al., U.S. Pat. No. 4,426,436 (issued Jan. 17, 1984), discloses a process for rapidly charging uncharged toner particles to a positive polarity.
Gruber et al., U.S. Pat. No. 4,415,646 (issued Nov. 15, 1983), discloses nitrogen containing polymers as charge enhancing additive for toners.
Williams, U.S. Pat. No. 4,299,898 (issued Nov. 10, 1981), discloses positively charged toners containing quaternary ammonium salts attached to acrylate polymers.
Horton, Xerox Disclosure Journal, Vol. 2, No. 1, p. 75 (January/February 1977), discloses a carrier coating with ionomeric resins.
Developer compositions with charge enhancing additives are well known. Thus, for example, there are described in U.S. Pat. Nos. 3,893,935; 4,937,157; and 4,904,762 the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions. Also, there is disclosed in U.S. Pat. No. 4,338,390 developer compositions containing as charge enhancing additives organic sulfate and sulfonates, which additives can impart a positive charge to the toner composition. Further, there is disclosed in U.S. Pat. No. 4,298,672 positively charged toner compositions with resin particles and pigment particles, and as charge enhancing additives alkyl pyridinium compounds. Moreover, toner compositions with negative charge enhancing additives are known, reference for example U.S. Pat. Nos. 4,411,974 and 4,206,064. The '974 patent discloses negatively charged toner compositions comprised of resin particles, pigment particles, and as a charge enhancing additive or-tho-halo phenyl carboxylic acids. Similarly, there are disclosed in the '064 patent toner compositions with chromium, cobalt, and nickel complexes of salicylic acid as negative charge enhancing additives.
Accordingly, there thus continues to be a need for improved charge control agents for incorporation into toner compositions and developer compositions. Additionally, there continues to be a need for charge control agents which effectively eliminate or passivate the contribution of pigments or other toner constituents to the triboelectric properties of positive and negative charging toner compositions. Also, there continues to be a need for toner and developer compositions which contain charge control agents that are non-toxic, do not adversely affect fuser rolls, and in particular Viton.RTM. fuser rolls selected for use in electrostatographic imaging systems, are thermally stable; and wherein the charge control agents are immobile. Additionally, there is a need for charge control agents which can be prepared by a simple direct, economical process, thereby decreasing the cost of the toner compositions generated. Furthermore, there continues to be a need for toner compositions which will rapidly charge new uncharged toner particles which are added to a positively charged toner composition or negatively charged toner compositions. Moreover, there continues to be a need for toner compositions comprised of charge control agents which will allow development of electrostatic latent images, either positively charged or negatively charged, with a wide spectrum of toner resins.